most of the time, whether it's only position 4 working or not working at all, it's probably the blower resistor or the plugs, here's what to look for.
start off by checking your fuses by the driver side door (most people probably already done this)
check the 30a fuse as well, replace fuse if blown.
not blown? don't panic, there's couple simple things to check.
first, check the blower resistor plug, is it plugged in? (see below to see where it's located if you don't know)
if the blower resistor plug is plugged in check the one behind the glove box (no idea what it actually is) (see below to see where it's located if you don't know)
to take out the glove box, pull the bottom right corner first, the rest will kinda follow, there's no need to flex the sides or anything like that. (in the picture you can see it's different from the other 3 corners)
everything plugged in and still not working? try replacing the blower resistor.
to do this unplug the blower resistor plug, then the plug on the blower motor, then there's one on the side.
the easiest way to get to this is to take off the panel on the side (between the dash and the door)
still not working? the next step is to replace the selector unit.
the easiest way to do this is to take off the top panel (the one going across the top over to the gauge cluster) then unhooking all the cables at the end (the end not connecting to the selector unit itself) undoing the 2 front screws and pulling it out, unhooking the 2 plugs.
unfortunately i don't have pictures of this because i never had to do it on my own car, i did it at the junkyard to see how the front dash went together/apart without the risk of damaging my own dash.
if you don't understand something, feel free to ask, i know i don't have the best grammar, or spelling for that matter.
hope this helps someone.
Many years later.... A big thank you for this!
